Hydrocarbons in the form of petroleum deposits and oil reservoirs are distributed worldwide. These oil reservoirs are measured in the hundreds of billions of recoverable barrels. Because heavy crude oil has a relatively high viscosity and may adhere to surfaces, it is essentially immobile and cannot be easily recovered by conventional primary and secondary means.
Microbial Enhanced Oil Recovery (MEOR) is a methodology for increasing oil recovery by the action of microorganisms (Brown, L. R., Vadie, A. A, Stephen, O. J. SPE 59306, SPE/DOE Improved Oil Recovery Symposium, Oklahoma, Apr. 3-5, 2000). MEOR research and development is an ongoing effort directed at discovering techniques to use microorganisms to benefit oil recovery (Sunde. E., Beeder, J., Nilsen, R. K. Torsvik, T., SPE 24204, SPE/DOE 8th Symposium on enhanced Oil Recovery, Tulsa, Okla., USA, Apr. 22-24, 1992). An effective MEOR treatment for crude oil desorption and mobilization could utilize microbially derived surface active agents (McInerney, M. J., et al., Development of microorganisms with improved transport and biosurfactant activity for enhanced oil recovery. DE-FE-02NT15321. DOE, 2003). Few have been identified that have been shown to alter the surface interaction between hydrocarbons and rocks, soil, brine, sand or clay to which the hydrocarbons are adhered.
Use of surface active agents or surfactants to increase solubility of oil through reduction in surface and interfacial tensions is another technique for increasing oil recovery. A wide variety of surfactants identified thus far are able to significantly reduce surface and interfacial tensions at the oil/water and air/water interfaces. Because surfactants partition at oil/water interfaces, they are capable of increasing the solubility and bioavailability of hydrocarbons (Desai, J. D. and I. M. Banat. Microbial production of surfactants and their commercial potential. Microbiol. Mol. Biol. Rev., 47-64, 1997 and Banat, I. M. Bioresource Technol. 51: 1-12, 1995 and Kukukina, M. S., et al. Environment International. 31: 155-161, 2005 and Mulligan, C., Environmental Pollution. 133: 183-198, 2005). Doong and Lei (J. Hazardous Materials. B96: 15-27, 2003), for example, found that the addition of surfactants to soil environments contaminated with polyaromatic hydrocarbons increased the mineralization rate of some hydrocarbons (Doong, R and W. Lei, supra). Such surfactants are expensive and may pose environmental or other equipment issues.
Biosurfactants, (biologically produced surfactants), have helped to substantially increase oil recovery from sandstone deposits by increasing solubility and decreasing viscosity of the oil (Mulligan, C., supra). Depending on the application, biosurfactants may be preferred since they are generally more biodegradable and less toxic than synthetically produced surfactants, and are effective under a broad range of oil and reservoir conditions. Examples of biosurfactants include glycolipids, lipopeptides and lipoproteins, fatty acids and phospholipids, polymeric compounds, and particulate biosurfactants (Desai, J. D. supra). However, further characterization of production and use of biosurfactants is needed. Further, there is a need to identify microorganisms that are able to produce these biosurfactants under reservoir conditions or other relevant environmental conditions.
Certain microorganisms have been described as having properties that may benefit MEOR processes. Certain Shewanella species have been disclosed as useful for remediation of metal contamination (U.S. Pat. No. 6,923,914B2), iron containing mixed waste (U.S. Pat. No. 6,719,902B1), manganese contamination (U.S. Pat. No. 6,350,605B1), and other pollutants with the aid of butane (U.S. Pat. No. 6,245,235B1). In EP1189843, certain Shewanella species were described as being useful for bioremediation of petroleum contaminants aerobically. In addition, Shewanella supplemented with butane was used for reduction of fouling in injection and recovery wells under aerobic conditions (U.S. Pat. No. 6,244,346B1). Other Shewanella species have been described as having the ability to produce biofilms (D. Bagge, et al., Appl. Environ. Microbiol. 67, 2319-2325. 2001); to sequester gases, in particular CO2, in underground geological formations and prevent their release into the atmosphere (see US20060216811A1); and to enhance oil recovery (commonly owned and co-pending US 2009-0260803 A1). The activity reported by these microorganisms is related to the degradation and transformation of hydrocarbons and other pollutants and not related to altering the interfacial boundaries between hydrocarbons and the surfaces to which they are bound.
The problem to be solved therefore, relates to the identification of microorganisms that: 1) have the ability to alter the interface between hydrocarbons and rock or other surfaces subject to coating by oil; 2) can be inoculated under suitable conditions which effect these alterations in surface properties; and 3) can be used in a cost-efficient way, to improve oil recovery, and benefit bioremediation.